Certain locking gearsets can switch between an engaged and disengaged state. A vehicle differential carrier (commonly known merely as a “differential”) contains such a type of gear. As context, the differential employs differential gears therein, which typically are connected to its exterior by three shafts. An input shaft transmits torque and rotation into the differential gears from a vehicle engine. In turn, each of the other two shafts separately transmit a portion of the torque and rotation from the differential gears out to separate external wheels. Regarding the operation of the differential, when a vehicle is being driven straight the differential rotates with an axle, while side and pinion gears mate but do not rotate relative to each other. However, when the vehicle turns the differential still rotates but the side and pinion gears mate and slightly rotate so that one wheel can turn faster than the other.
Hence, the differential is needed because when a vehicle is turning, as it quite often does, the outside wheel makes a larger radius than the inside wheel. As a result, the outside wheel goes a farther distance, moves faster and turns more revolutions than the inside wheel. If, however, both wheels were on the same axle shaft, in this instance, one or both wheels would have to skid or slip to make a turn. Consequently, the function of the differential allows the wheels to turn at different speeds, but at equal torque.
In certain situations it is desirable to lock the differential so that the two wheels on an axle are restricted to the same rotational speed without regard to available traction or differences in resistance seen at each wheel.
Control of the locking of the differential involves several actions. Engagement of the differential is controlled by an actuator assembly. The actuator assembly is powered and signaled by the vehicle through a controller. As is known in the art, the actuator assembly contains, along with other components, a solenoid which converts electrical current into a mechanical force. The flow of electrical current through the coil of the solenoid creates a magnetic field that moves the magntoresponsive plunger of the solenoid, and thereby engaging or disengaging the actuator assembly, and therefore the gearset.
In addition, it is beneficial to have a sensor that can relay information regarding the mode of the actuator assembly back to the controller. A sensor provides a signal that is indicative of the engaged/disengaged mode of the actuator assembly. The technology described herein relates to such a sensor. These sensors are sometimes referred to as switches or positional switches.
Prior art mechanical positional sensors can have wear or mounting issues. Magnetic proximity sensors can have accuracy problems based on runout and are subject to interfering fields from adjacent electromagnetic solenoid. However, the proposed solution herein has no mechanical contact with moving parts, is less sensitive to runout, and can be made less sensitive to external magnetic fields.
The current design employs the known Hall type sensor (also known as a Hall element) using vane interruption. A Hall type sensor is a transducer that varies its output voltage in response to a magnetic field. Hall effect sensors are used extensively for proximity switching, positioning, speed detection, and current sensing applications. If the magnetic field near the Hall type sensor is interrupted or disturbed, the output voltage varies accordingly. Vane interruption is achieved when a ferrous material (the vane) is placed in between a magnet producing a magnetic field and the Hall sensor. The basic principal of this effect is shown in FIGS. 1A and 1B. FIG. 1A shows a magnet 10 producing a magnetic field 20 that can be sensed by the Hall sensor 30. FIG. 1B shows the magnetic field 20 being interrupted by a vane of ferrous material 40. The current design utilizes this principle to create a positional sensor for a locking gearset, such as a differential.
Advantageously, the current design is largely insensitive to runout of the moving part being sensed. Another advantage of the embodiments described herein is that different sensor orientations are possible to minimize magnetic field interference from the solenoid. Concentrators can be used to direct the sensor field and increase efficiency. In addition, some magnet orientations that can be used in the embodiments described herein can be coated in a thicker layer of non-magnetic material, reducing pick-up of ferrous particles.